1. Field of the Invention
The present invention relates to a recording and reproducing apparatus for image signals such as a video-tape-recorder (VTR).
2. Description of the Prior Art
VTRs which record video-signals, such as signals of a black and white television and a color television on a magnetic tape and reproduce the same, especially a helical VTR which records video signals for one field element on one oblique track, have been used not only for broadcasting but for home use application and other applications. They are also used in a portable video system together with a simple video camera. When new video signals are to be recorded on a tape while the tape is being run in such helical VTR after video signals are recorded on a portion of the tape or a portion of the tape is reproduced and the tape is stopped once, if intervals of control signals (CTL signals) recorded on a control track are not uniform at joints between a recording locus already formed on the tape and a recording locus subsequently formed thereon, a disturbance in synchronism will take place at the joints as both recording loci are reproduced in succession. This presents an unsightly reproduction.
Various countermeasures have been proposed and put in practical uses for eliminating this phenomenon. For example, in a so-called phases matching system, an apparatus has been proposed such that when a tape is changed over from a running mode to a stopped mode, a certain amount of tape is rewound and then is stopped, and as a next recording is started, first, after the apparatus is started with a reproduction mode, a change over is not immediately made to a recording mode. Instead a driving adjustment of a capstan is made before shifting to a next recording mode, so that phases of control signals for a next recording and control signals for reproduction match each other at this time.
In this method, the apparatus needs to make a series of sequence actions running.fwdarw.rewinding.fwdarw.stopping and stopping.fwdarw.synchronizing in reproduction.fwdarw.recording, and means to enable the capstan to make positive and reverse rotations will be necessary, thus a mechanism and circuit will become complicated, increasing manufacturing cost thereof. Also, since the tape is rewound for a prescribed amount, there are shortcomings that other video signals are recorded on the previous recording locus and other previous recordings are erased.
As a simpler method than this phases matching system, a so-called timing phases system has recently been used for a home use VTR, etc. This system has a circuit to detect a timing of a control pulse immediately after a change over action to change over a tape from a running state to a stopped state or in a reverse, and a delay circuit to delay an output from said detection circuit for a length of time as corresponding to a mechanical delay in a tape driving system. The tape driving system is controlled by an output of the delay circuit so that the tape is changed over from a running state to a stopped state or in a reverse thereto in synchronism with a control signal pulse. In this system, both mechanical down time from a running state to a stopped state and a mechanical rise time from a stopped state to a running state need to be sufficiently small compared to a cycle of frames. Therefore, an apparatus using this system has many restrictions in mechanical designing and requires close and fine care and control in assembly operations. In addition, adjustments of respective delay circuit for the change over from the running to the stopped state and from the stopped to the running state are difficult.